sorry I play SAM. SAM does more dps when they can actually stay on the mob rather than running only over the place avoiding Aoes. It's a bad idea just to mass pull and I've seen it kill many a group unnecessarily

you don't save anytime at all by pulling 20mobs at the same time. you just put your group in danger. Like you have explained there are many factors here required to make this 20mobs mass pulling work.

General rule in life is the more factors required to make something work the higher chance it has to fail.

so keep it simple in general. The fact is every tank thinks he has what it takes to make it work. I've seen this false statement on these forums before.
i.e
I'm a tank and I always check gear and class make up

I've played this game since launch. I have yet to see one tank do that. It's a lie you guys make up to justify a bad habit. no one does.

you simply charge in and ask everyone to pick up the pieces.